In the long term, Mayer can't afford for Yahoo Mail to break down and shed individual users or lose partnerships with major ISPs.

Yahoo Mail is one of Yahoo's two most important products, along with the homepage.

Yahoo has hundreds of millions of mail users. Yahoo makes a lot of money off these users because they often end up looking at other ad-supported Yahoo pages, including Yahoo.com, before or after they check their email.

Thanks to the user migration to non-Web-based, mobile email, Yahoo is beginning to see fewer of these money-making sessions. It can't afford to accelerate the process with bad product.

The good news for Mayer is that thanks to Yahoo's lucrative investment in Asian Internet companies, she has lots of time to fix Yahoo Mail and the development structure that resulted in a flawed product.